1. Field
One embodiment of the present invention relates to a printed circuit board on which a semiconductor package is mounted.
2. Description of the Related Art
In an electronic apparatus such as a personal computer, a circuit board, on which a squared large-sized semiconductor package of several-ten millimeters in each side that constitutes a CPU and its peripheral circuits, is accommodated in the casing as a main structural element.
In the circuit board that is used in this type of electronic apparatus, such as a personal computer, protection means is needed for protecting a mounting surface of the semiconductor package from a stress which is applied due to warp or deformation of the board, or shock or vibration from outside.
As means for protecting solder bonding portions of a component, which is mounted on the board, from stress, there is known an electronic component mounting method in which an under-filler (thermoplastic resin) is inserted between the board and a semiconductor chip, so that the gap between the board and the semiconductor chip is filled with the under-filler, thereby fixing the semiconductor chip on the board. See, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-357714.
In the case where the above-described reinforcement means using the under-filler to the above-described circuit board on which the large-sized semiconductor package is amounted, the reinforcement material, which is filled as the under-filler between the semiconductor package and the board, repeats thermal expansion due to self-heat-production resulting from the circuit operation of the semiconductor package. The thermal expansion causes a problem that an excessive stress acts on the solder bonding portions. In particular, in a circuit board on which a large-sized BGA (ball grid array) is mounted, stress concentrates at corner portions of a rectangular package, causing circuit breakage of the solder bonding portions. This problem is more conspicuous as the thermal expansion coefficient of the reinforcement material filled as the under-filler is more different from that of the semiconductor package or the board. Besides, since the entire mounting surface of the large-sized semiconductor package is bonded to the board, there arises such a problem that rework becomes difficult.
In the mounting technology of BGA, it has conventionally been thought that when the above-described reinforcement means by bonding is used, the adhesive mixes in solder balls and the strength of solder bonding decreases. To cope with this, various measures have been taken in order to prevent mixing of the adhesive in the solder balls. Specifically, the amount of the adhesive (reinforcement material) is decreased or the bonding position is displaced so that the solder balls may not deform, thereby preventing the adhesive from entering the solder balls.
According to an aspect of the present invention, there is provided a printed circuit board comprising: a printed wiring board having a component mounting surface; a semiconductor package which is mounted on the component mounting surface of the printed wiring board by solder bonding using solder balls; and reinforcement portions which locally reinforce portions of the solder bonding of the semiconductor package at a plurality of locations on the component mounting surface of the printed wiring board, the reinforcement portions being formed of a resin material having parts entering the solder balls of the portions of the solder bonding.